Formation and Evolution of Early Precambrian Continental Crust in Alxa Block     

Luo Zhibo 《地球科学进展》2015,30(8):878-890

By the analysis of the published zircon U-Pb ages and Hf isotope data, this paper firstly presents a comprehensive review about the staggered growth and reworking of early Precambrian continental crust in Alxa Block. The results show that the ancient crustal remnants of Alxa Block was formed in Meso-Paleo Archean, which was recorded by 3.0~3.6 Ga detrital zircons and Hf model ages. The early crustal growth of Alxa Block could be traced back to early Paleo-archean. Currently, the oldest zircon U-Pb age is about 3.6 Ga. Analogous to the other places of North China Craton, the Alxa Block underwent two-stage crustal growth at 2.7~2.9 Ga and 2.5~2.6 Ga respectively, and the former might be wider. The ~2.5 Ga (TTG) tectono-magmatic event, which represents the North China continent’s cratonization, also existed in Alxa Block. The corresponding zircon Hf isotope data indicate that the TTGs were mainly derived by melting of 2.7~2.9 Ga juvenile crust, possibly by mixing with a certain ancient crust, and a small portion was produced by instant reworking of 2.5~2.6 Ga juvenile crust. Proceeding to Paleo-proterozoic, the Alxa Block underwent multi-stage tectono-magmatic events, approximately peaked at 2.30~2.35 Ga, 2.15~2.17 Ga, 2.00~2.10 Ga, 1.95~1.98 Ga and ~1.90 Ga. The continental crust was mainly formed by reworking of 2.7~2.9 Ga and 2.5~2.6 Ga juvenile crust, simultaneously by a fraction of ~2.1 Ga juvenile crust. In Paleo-proterozoic, not only the Archean crustal reworking but also the juvenile crustal growth existed in Alxa Block.  相似文献   

Radio variability of the blazar S5 0716+714: a ∼6.1 year quasi-periodicity     

Xiao-Pan Li  Yu-Hui Luo  Hai-Yan Yang  Cheng Yang  Yan Cai  Hai-Tao Yang  Li Zhou  Yu-Qiong Shan 《Astrophysics and Space Science》2018,363(8):169

We report a ～6.1 yr quasi-periodicity for the blazar S5 0716+714 using the radio light curves at 4.8, 8 and 14.5 GHz observed by the University of Michigan Radio Astronomical Observatory (UMRAO) from 1981 to 2012, by means of the Jurkevich, discrete correlation function (DCF) and power spectral analysis techniques. There are a general correlation among light curves at different frequencies and a time lag of \(170\pm 10\) days between 4.8 and 14.5 GHz light curves can be confirmed. We also estimate the orbit parameters assuming a binary black hole system, and the magnetic field strength under the jet comoving frame.  相似文献   

应用Hydrolight模式研究含油水体辐射传输特性的关键技术          下载免费PDF全文

黄妙芬  骆蔚健  刘杨  邢旭峰  庄炀 《海洋技术学报》2019,38(3):7-14

辐射传输模式Hydrolight在国际水色遥感研究领域已被广泛用于解决水体光学的各种问题,也是进行石油类污染水体辐射传输特性研究的有效模型。结合Hydrolight模式的机理、应用现状及含油水体的特点,提出了将该模式应用于光学特性复杂的石油污染水体辐射传输特性研究时需要解决的关键技术,包括测定石油污染水体吸收系数和散射系数、建立石油污染吸收和散射特性随波长和深度变化的参数化模型、确定油物质的吸附后悬浮颗粒物体散射函数模型等方面。依据2018年8月和2016年8月分别在辽宁大连港和辽宁盘锦辽河油田等区域测定的含油水体数据,讨论了这些关键技术的解决方案。  相似文献   

The relationship between significant wave height and Indian Ocean Dipole in the equatorial North Indian Ocean     

Chen Fu  Dongxiao Wang  Lei Yang  Yao Luo  Fenghua Zhou  Tilak Priyadarshana  Jinglong Yao 《Ocean Dynamics》2018,68(6):689-699

Based on reanalysis data, we find that the Indian Ocean Dipole (IOD) plays an important role in the variability of wave climate in the equatorial Northern Indian Ocean (NIO). Significant wave height (SWH) in the equatorial NIO, especially over the waters southeast to Sri Lanka, exhibits strong interannual variations. SWH anomalies in the waters southeast to Sri Lanka correlate well with dipole mode index (DMI) during both summer and autumn. Negative SWH anomalies occur over the oceanic area southeast to Sri Lanka during positive IOD events and vary with different types of IOD. During positive prolonged (unseasonable) IOD, the SWH anomalies are the strongest in autumn (summer); while during positive normal IOD, the SWH anomalies are weak in both summer and autumn. Strong easterly wind anomalies over the southeast oceanic area of Sri Lanka during positive IOD events weaken the original equatorial westerly wind stress, which leads to the decrease in wind-sea waves. The longer wave period during positive IOD events further confirms less wind-sea waves. The SWH anomaly pattern during negative IOD events is nearly opposite to that during positive IOD events.  相似文献   

Rock Burst Intensity Classification Based on the Radiated Energy with Damage Intensity at Jinping II Hydropower Station,China     

Bing-Rui Chen  Xia-Ting Feng  Qing-Peng Li  Ru-Zhou Luo  Shaojun Li 《Rock Mechanics and Rock Engineering》2015,48(1):289-303

  相似文献   

The effect of expansion ratio on the critical Reynolds number in single fracture flow with sudden expansion          下载免费PDF全文

Jiazhong Qian  Lei Ma  Hongbin Zhan  Qiankun Luo  Xiao Wang  Mu Wang 《水文研究》2016,30(11):1718-1726

Flow in a single fracture (SF) is an important research subject in groundwater hydrology, hydraulic engineering, radioactive nuclear waste repository and geotechnical engineering. An abruptly changing aperture is a unique type of SF. This study discusses the relation between the values of the critical Reynolds number (Re_c) for the onset of symmetry breaking of flow and the expansion ratio (E) of SF, which is defined as the ratio between the outlet (D) and inlet (d) apertures. This study also investigates the effect of inlet aperture d on Re_c for flow in an SF with abruptly changing apertures (SF‐ACA) using the finite volume method. Earlier numerical and experimental results showed that flow is symmetric in respect to the central plane of the SF‐ACA at small Reynolds number (Re) but becomes asymmetric when Re is sufficiently large. Our simulations show that the value of Re_c decreases with the increasing E, and the relationship between the logarithm of Re_c and E can be described accurately using either a quadratic polynomial function or a logarithmic function. However, the relationship of Re_c and d for a given E value is vague, and Re_c becomes even less sensitive to d when E increases. This study also reveals that the hydraulic gradient (J) and flow velocity (v) follow a super‐linear relationship that can be fitted almost perfectly by the Forchheimer equation. The inertial component (J_i) of J increases monotonically with Re, whereas the viscous component (J_v) of J decreases monotonically with Re. The Re value corresponding to equal inertial and viscous components of J (named as the transitional point Re) decreases when E increases, and such a transitional point Re should be closely related to the critical Reynolds number Re_c, although a rigorous theoretical proof is not yet available. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

An alternative Boussinesq equation considering the effect of hysteresis on coastal groundwater waves          下载免费PDF全文

Jun Kong  Zhaoyang Luo  Chengji Shen  Guofen Hua  Hongjun Zhao 《水文研究》2016,30(15):2657-2670

This paper presents an alternative Boussinesq equation considering hysteresis effect via a third‐order derivative term. By introducing an improved moisture–pressure retention function, this equation describes, with reasonable precision, groundwater propagation in coastal aquifers subject to Dirichlet boundary condition of different oscillation frequencies. Test results confirmed that it is necessary to consider horizontal and vertical flows in unsaturated zone, because of their variable influences on hysteresis. Hysteresis in unsaturated zone can affect the water table wave number of groundwater wave motion, such as wave damping rate and phase lag. Oscillations with different periods exert different hysteresis effect on wave propagation. Truncation/shrinkage of unsaturated zones also affects the strength of hysteresis. These impacts can be reflected in the alternative Boussinesq equation by adjusting the parameter representing the variation rate of moisture associated with pressure change, as opposed to traditional computationally expensive hysteresis algorithms. The present Boussinesq equation is simple to use and can provide feasible basis for future coupling of groundwater and surface water models. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Influence of Fluctuating Groundwater Table on Volatile Organic Chemical Emission Flux at a Dissolved Chlorinated-Solvent Plume Site     

Yuanming Guo  Chase Holton  Hong Luo  Paul Dahlen  Paul C. Johnson 《Ground Water Monitoring & Remediation》2019,39(2):43-52

Groundwater elevation fluctuation has been recognized as one mechanism causing temporal indoor air volatile organic chemical (VOC) impacts in vapor intrusion risk assessment guidance. For dissolved VOC sources, groundwater table fluctuation shortens/lengthens the transport pathway, and delivers dissolved contaminants to soils that are alternating between water saturated and variably saturated conditions, thereby enhancing volatilization potential. To date, this mechanism has not been assessed with field data, but enhanced VOC emission flux has been observed in lab-scale and modeling studies. This work evaluates the impact of groundwater elevation changes on VOC emission flux from a dissolved VOC plume into a house, supplemented with modeling results for cyclic groundwater elevation changes. Indoor air concentrations, air exchange rates, and depth to groundwater (DTW) were collected at the study house during an 86-d constant building underpressurization test. These data were used to calculate changes in trichloroethylene (TCE) emission flux to indoor air, during a period when DTW varied daily and seasonally from about 3.1 to 3.4 m below the building foundation (BF). Overall, TCE flux to indoor air varied by about 50% of the average, without any clear correlation to changes in DTW or its change rate. To complement the field study, TCE surface emission fluxes were simulated using a one-dimensional model (HYDRUS 1D) for conditions similar to the field site. Simulation results showed time-averaged surface TCE fluxes for cyclic water-table elevations were greater than for stationary water-table conditions at an equivalent time-averaged water-table position. The magnitudes of temporal TCE emission flux changes were generally less than 50% of the time-averaged flux, consistent with the field site observations. Simulation results also suggested that TCE emission flux changes due to groundwater fluctuation are likely to be significant at sites with shallow groundwater (e.g., < 0.5 m BF) and permeable soil types (e.g., sand).  相似文献   

A modified domain reduction method for numerical simulation of wave propagation in localized regions     

Luo  Chao  Lou  Menglin  Gui  Guoqing  Wang  Hao 《地震工程与工程振动(英文版)》2019,18(1):35-52

A modified domain reduction method(MDRM) that introduces damping terms to the original DRM is presented in this paper. To verify the proposed MDRM and compare the computational accuracy of these two methods, a numerical test is designed. The numerical results of the MDRM and DRM are compared using an extended meshed model. The results show that the MDRM significantly improved the computational accuracy of the DRM. Then, the MDRM is compared with two existing conventional methods, namely Liao's transmitting boundary and viscous-spring boundary with Liu's method. The MDRM shows its great advancement in computational accuracy, stability and range of applications. This paper also discusses the influence of boundary location on computational accuracy. It can be concluded that smaller models tend to have larger errors. By introducing two dimensionless parameters, φ_1 and φ_2, the rational distance between the observation point and the MDRM boundary is suggested. When φ_1 2 or φ_213, the relative PGA error can be limited to 5%. In practice, the appropriate model size can be chosen based on these two parameters to achieve desired computational accuracy.  相似文献   

Use of four drought indices for evaluating drought characteristics under climate change in Shaanxi,China: 1951–2012     

Rengui Jiang  Jiancang Xie  Hailong He  Jungang Luo  Jiwei Zhu 《Natural Hazards》2015,75(3):2885-2903

  相似文献